The present invention relates to the modification of various materials, and more particularly to incorporation of antioxidants in asphalt binders to lower their oxidative aging.
Asphalt concrete is a composite material that is commonly used for construction of pavement. More than 95% of all pavements in service today incorporate asphalt concrete. Asphalt concrete includes an asphalt binder and mineral aggregate. The binder and aggregate are mixed together and then layered down and compacted.
The asphalt binder deteriorates during hot-mix production and service because of oxidative hardening. Oxidative hardening occurs as a result of the asphalt binder readily undergoing oxidation when it reacts with atmospheric oxygen at elevated temperatures. Asphalt binder is a hydrocarbon which generally consists of about 85% carbon, 10% hydrogen, 5% heteroatoms, and trace elemental atoms. The heteroatoms, which include sulfur, oxygen, and nitrogen, can form reactive functional groups that accelerate the oxidation process. The trace metals, which include vanadium, nickel, and iron, can act as catalysts for the oxidation reaction.
Furthermore, oxidation is an irreversible chemical reaction that can occur throughout the life of an asphalt pavement such as during mixing, field placement, and during service. Excessive oxidation of the asphalt may potentially cause the asphalt to harden, become brittle, and ultimately crack over time. This stiffening mechanism of the asphalt is also commonly termed “age hardening.”
Currently, no effective treatments exist to control the excessive age hardening of the asphalt binder. Accordingly, there remains a need to increase the durability of the asphalt binder by reducing its oxidative age hardening.